1. Field of the Invention
The subject invention is directed to a power distribution architecture for an ice protection system in an aircraft, which minimizes wire weight while distributing by-product waste power to several line replaceable units.
2. Description of Related Art
Since the early days of powered aviation, aircraft have been troubled by the accumulation of ice on critical component surfaces such as wings and struts, under certain flight conditions. Unchecked, accumulations of ice can eventually so laden an aircraft with additional weight and so alter the aerofoil configuration of the wings as to precipitate an unacceptable flying condition. There are three generally accepted approaches that have been developed to combat the accumulation of ice on component surfaces of an aircraft under flying conditions. These approaches include thermal de-icing, chemical de-icing and mechanical de-icing.
In the case of thermal de-icing, leading edges (i.e., the edges of an aircraft component on which ice accretes and are impinged upon by the air flowing over the aircraft and having a point at which this airflow stagnates) are heated to loosen adhesive forces between accumulating ice and the component. Once loosened, the ice is blown from the component surface by the airstream passing over the aircraft.
In one thermal de-icing approach, a heating element is placed in the leading edge zone of the component or by incorporation into the skin structure of the component. This heating element is typically powered by electrical energy derived from a generating source driven by one or more of the aircraft engines. The electrical energy is intermittently or continuously supplied to provide heat sufficient to prevent the formation of ice or to loosen accumulating ice. An example of a heating element for a thermal de-icing system is described in U.S. Pat. No. 5,351,918 to Giamati et al., the disclosure of which is incorporated herein by reference in its entirety.
A baseline prior art thermal de-icing system for an engine inlet (or nacelle) of an aircraft is illustrated in FIG. 2 of the subject application and is designated generally by reference numeral 10. De-icing system 10 includes controller 12 located in the aircraft fuselage 14. Controller 12 has two communication channels (channel A, channel B) and each communicates with a plurality of power distribution units (PDUs) 16a-16c located within the engine nacelle 18 through respective communication lines 20a, 20b. More particularly, controller 12 is adapted and configured to control the supply of energy delivered from the PDUs 16a-16c to heating element segments 22a-22c embedded within the lip or leading edge 24 of the engine nacelle 18 for ice removal.
The power distribution units 16a-16c receive power from a point of regulation (POR) 26 located within the aircraft fuselage 14. More particularly, three-phase power is delivered from the POR 26 to the PDUs 16a-16c through a single primary power cable 28. In this example, power cable 28 extends approximately 80 feet from the POR 26, through the fuselage 14, aircraft wing 30 and pylon 32, to a junction box 34 located in or near engine nacelle 18. Secondary power cables 38a, 38b and 38c (each averaging about 7.67 feet in length, in this example) extend from junction box 34 to the PDUs 16a-16c. 
Because the primary power cable 28 is carrying three-phase power, it includes four individual wires, including three power-carrying wires and one neutral wire. The weight of these wires is a dominant factor in the overall weight of the de-icing system 10, and is a significant factor to be taken into account in designing and optimizing such a system.
Wire weight is determined using MIL-W-5088L. More particularly, in the exemplary ice protection system of FIG. 2, the three-phase line current would be 67 A. Derating the wire in accordance with MIL-W-5088L for 25,000 ft. altitude operation at 25° C. and a four-conductor power feed system with 75% utilization (i.e., 3 of the 4 wires in cable 28 carry power) yields a requirement for AWG 8 wire. In the present example, power cable 28 includes about 80 feet of three phase AWG 8 wire, which weighs about 18.4 lbs. This constitutes 95% of the prior art system wiring weight and is significant.
An additional design consideration in a de-icing system such as that which is shown in FIG. 2, is the weight of the power distribution units, which are line replaceable units (LRU), and by-product power dissipation from the LRUs. Both excess weight and LRU power dissipation are undesirable characteristics of a typical thermal de-icing system. Power dissipation requires large heat sinks, which add to the weight of the LRU. Moreover, heat sinks are largely ineffective at higher altitudes. The LRUs in the exemplary prior art de-icing system of FIG. 2 (i.e., the dual channel controller 12a, 12b and power distribution units 16a-16c) collectively weigh about 79 lbs. The estimated by-product power dissipated for each nacelle-based PDU in this example is about 56W.
Given the design deficiencies associated with the prior art baseline de-icing system exemplified in FIG. 2, it would be beneficial to design a thermal de-icing system for an aircraft, which minimizes wire weight of the power cables feeding the LRUs and effectively distributes by-product waste power to multiple LRUs in a manner that minimizes LRU heat rise.
In overcoming the deficiencies of the prior art baseline de-icing system, the subject invention provides the power distribution architecture of an ice protection system that optimizes system weight (i.e., wire weight and LRU weight) while efficiently distributing by-product waste power amongst several LRUs. Moreover, by employing the novel power distribution architecture of the subject invention, which locates the anti-ice power distribution function within the aircraft fuselage, the power dissipation per nacelle-based PDU is decreased and the bulk of the by-product waste power dissipation for the system is moved from the nacelle, where space is limited and air may be thinner, to the aircraft fuselage where the environment is more conducive to by-product power dissipation.